Field of the Invention
The present invention relates to, for example, a substrate for use in making a semiconductor device and to a method of manufacturing the substrate.
Background Art
Various kinds of processing are performed on a semiconductor substrate to make on the substrate a circuit having components such as transistors, resistors and capacitors. For example, a metal thin film or an insulating film is formed on a substrate by a semiconductor manufacturing apparatus and a resist is patterned by an exposure apparatus.
In a wafer process in which various kinds of processing are performed on a substrate, the presence/absence of the substrate is detected with a substrate recognition sensor in a semiconductor manufacturing apparatus. For detection of the presence/absence of an Si or GaAs substrate, the property of the substrate to absorb (or reflect) red light or infrared light is utilized. More specifically, the absence of the substrate is recognized when red light or infrared light is incident on the sensor. Also, the presence of the substrate is recognized when red light or infrared light is absorbed by the substrate and is not incident on the sensor.
In recent years, a compound semiconductor substrate such as an SiC or GaN substrate having a bandgap wider than that of Si has been put to use in a power device or a radiofrequency device in some cases. Since SiC or GaN is transparent to red light or infrared light, the presence/absence of the substrate cannot be detected by means of red light or infrared light.
Japanese Patent Laid-Open No. 2010-141124 discloses an arrangement in which a total reflecting surface provided on an end portion of a substrate reflects red light or the like.
A semiconductor manufacturing apparatus used to process an Si or GaAs substrate or the like detects the presence/absence of the substrate by means of red light or infrared light. If a new detection system is constructed to detect a substrate transparent to red light or infrared light, the manufacturing cost is increased. It is, therefore, preferable to process a substrate transparent to red light or infrared light with an existing semiconductor manufacturing apparatus capable of detecting the presence/absence of a substrate transparent to red light or infrared light. The technique disclosed in Japanese Patent Laid-Open No. 2010-141124, however, uses a total reflecting surface provided on an end portion of a substrate and therefore has a problem of being incapable of detecting the presence/absence of the substrate at a central portion of the substrate.
A method of enabling detection of a substrate transparent to red light or infrared light by forming a metal thin film layer such as Cr, W or Al having a low transmittance with respect to red light or infrared light on the back surface of the substrate is conceivable. However, there is a possibility of the metal thin film layer being separated or etched in a process in which treatments such as heat treatment, dry etching, wet etching and treatment with a chemical solution are repeatedly performed.